1. Field of the Invention
The present invention relates to an air filter usable as a component part of an air cleaner that is disposed in an intake system of an internal combustion engine.
2. Description of the Related Art
In normally employed air cleaners, an air filter is firmly retained at a housing position by a construction in which a collar portion of a pleated filter body is clamped by a case and a cap that are detachable from each other. Such air filters are desired to be simply constructed and low-cost. U.S. Pat. No. 5,674,302 discloses a filter in which a pleated filter body and a collar portion (i.e., a portion to be clamped by a case and a cap) are formed from the same material. Japanese Patent Application Laid-Open No. HEI 8-243334 discloses a filter in which a collar portion of a pleated filter body (i.e., a portion to be clamped by a case and a cap) is formed by a hard portion and a soft portion, and the collar portion is clamped in such a manner that the position of the collar portion can be set by using a clamping portion of the case and a clamping portion of the cap. Toyota Technical Report No. 6865, published on May 30, 1997, discloses an air cleaner element mounting construction in which a filter element is mounted between a case and a cap in such a manner that a protrusion formed in a flange (clamping portion) of the cap that faces a clamping portion of the case is fitted to a corrugated portion formed inwardly of a seal portion of the element (i.e., a portion of the element that is clamped by the clamping portion of the case and the flange (clamping portion) of the cap). JIII Journal of Technical Disclosure No. 96-9626, published on Aug. 1, 1996, discloses a construction in which the positioning and sealing of a non-woven fabric-integrated air filter is improved by fitting a protrusion formed in a clamped portion of the air filter into a recess formed in a clamping portion of a case that faces a clamping portion of a cap.
However, the aforementioned air filters have not received consideration regarding prevention of a mounting error that where a filter element is to be mounted at such a position as to divide a space defined by the case and the cap into a dusty side and a clean side, that is, a before-filtration side and an after-filtration side, the filter element is falsely placed in a 180.degree.-reversed orientation so that the dusty and clean sides of the filter element are in the opposite positions (reversed positions). Therefore, the conventional air filters need an improvement in this respect.